There has been an approach to decrease the rolling resistance of a tire to suppress heat build-up and thus improve the fuel economy of a vehicle. The demand for improving the fuel economy of a vehicle from the aspect of tires has increased in recent years. The demand is particularly large for improving fuel economy from the aspect of improvement of a tread or sidewall among tire components. Also in recent years, heavy-load tires for trucks and buses as well as tires for passenger vehicles are needed to improve in terms of fuel economy.
Known methods for preparing a satisfactory rubber composition with less heat build-up include a method using semi-reinforcing filler and a method using a smaller amount of reinforcing filler. However, such methods for improving fuel economy by means of filler cause a reduction in the effect of reinforcing the rubber composition, and thereby disadvantageously reduce breaking performance. Therefore, it has been difficult to achieve both high levels of fuel economy (low rolling resistance) and breaking performance.
Meanwhile, natural rubber may be used in the production of a heavy-load tire, which generally needs mastication of natural rubber. Therefore, the use of natural rubber decreases productivity. Further, the mastication causes molecular chain scission in natural rubber, thereby disadvantageously leading to a loss of the properties (e.g., effects of improving fuel economy and rubber strength) of a high-molecular-weight polymer which natural rubber essentially has.
Patent Document 1 discloses a method of adding a proteolytic enzyme and a surfactant to natural rubber latex and maturing the latex. However, the composition still has room for improving fuel economy, breaking performance, and abrasion resistance in a balanced manner.
Patent Document 1: JP 2005-82622 A